Field of the Invention
The present invention relates to wireless communication.
Related Art
3rd generation partnership project (3GPP) long term evolution (LTE) evolved from a universal mobile telecommunications system (UMTS) is introduced as the 3GPP release 8. The 3GPP LTE uses orthogonal frequency division multiple access (OFDMA) in a downlink, and uses single carrier-frequency division multiple access (SC-FDMA) in an uplink. The 3GPP LTE employs multiple input multiple output (MIMO) having up to four antennas. In recent years, there is an ongoing discussion on 3GPP LTE-advanced (LTE-A) evolved from the 3GPP LTE.
As disclosed in 3GPP TS 36.211 V10.4.0 (2011-12) “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 10)”, 3GPP LTE/LTE-A may divide the physical channel into a downlink channel, i.e., a physical downlink shared channel (PDSCH) and a physical downlink control channel (PDCCH), and an uplink channel, i.e., a physical uplink shared channel (PUSCH) and a physical uplink control channel (PUCCH).
Meanwhile, in recent years, an environment for establishing a plurality of small-scaled cells (or small cells) or an environment simultaneously using a plurality of small cells or a macro cell may be considered or established.
In this case, the small cell may be used a primary cell (Pcell) of specific UE. A corresponding small cell may be used as only a secondary cell (S cell).
Further, recently, it is considered that the UE generates and transmits a new search signal in addition to an existing PSS (primary synchronization signal)/SSS (secondary synchronization signal) PSS (primary synchronization signal)/SSS (secondary synchronization signal) to efficiently find small cells which are densely located.
However, since a plurality of small cells are located in the same channel to be close to each other in the above small cell environment, interference between small cells may have a problem larger than that of interference of the macro cell.